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Microsoft Corp. is working with the OPC Foundation to enable almost any IIoT scenario using interoperability between the millions of OPC UA-compliant applications and equipment. Microsoft will enable IIoT users to connect manufacturing equipment and software with extended support of OPC UA's open-source software stack. Microsoft’s extended support for OPC UA spans its IoT offerings from local connectivity with Windows devices to cloud connectivity via Microsoft Azure. Integration with Azure IoT allows customers to easily send OPC UA data to the Azure cloud, as well as command and control OPC UA devices remotely from the Azure cloud.
Pepperl+Fuchs broke ground June 2 on its new U.S. distribution and engineering center in Katy, Texas, near…

While routine build-up and clogging in process applications is annoying, process scaling is more persistent, causes unplanned downtime and increases costs in many industries. It's typically composed of calcium carbonate, wax, grease or similar…

Just as you can't have too many friends, level measurement applications can't get enough ease of use, reliability and safety. Thanks to increasing process industry needs and user demand for them, these are the three unifying priorities that drove…

Our panel of experts explore best practices for dealing with buildup on chemical seals of a differential pressure flowmeter.

Q: We have a venturi flowmeter with 3-in. flanged pressure taps and flanged chemical seals with capillary tubes in a 44-in. vertical pipe (Figure 1). The fluid is hydrocarbon (polymeric) gas. The problem is that the chemical seal diaphragms often…

A Control Design reader writes: We have several temperature, pressure and flow sensors on a new medical-device cleaning skid that we are developing. These instruments are connected to a PLC as 4-20 mA inputs, and there is also a 4-20 mA output used to control a pump motor speed. A recent failure of a flow sensor brought the process skid instrumentation to my company's quality manager's attention. He asked how we know that the temperatures, pressure and flow are accurate, and how do we know that we are cleaning properly.
I've been tasked to write a procedure for troubleshooting, calibrating and testing the 4-20 mA instruments on the skid. I can probably stumble through this, but what are some best practices for troubleshooting the analog…

Control's Monthly Resource Guide brings you the latest online resources on a variety of process control topics.

MULTI-PART WEIGHING
This four-section webpage by Omega Engineering covers "Weighing Applications," "Weighing System Design," "Installation and Calibration" and "Specialized Installations." The whole group is located at…

FOPDT model has demonstrated utility for controller tuning rules, for structuring decouplers and feedforward control algorithms.

A first-order plus deadtime (FOPDT) model is a simple approximation of the dynamic response (the transient or time-response) of a process variable to an influence. It’s also called first-order lag plus deadtime (FOLPDT), or “deadtime” may be…

'To the degree networks and standards can provide easy, consistent and seamless access to device-resident controls, the vision of truly distributed control may finally dawn upon us.'

Every compressor in the facility went down at once that day, when a PLC redundancy switchover didn’t transfer in time. The engineers didn’t know that each P453 remote I/O processor had a dip-switch-selectable timeout setting—if it didn’t…

A Control Design reader writes: We have several temperature, pressure and flow sensors on a new medical-device cleaning skid that we are developing. These instruments are connected to a PLC as 4-20 mA inputs, and there is also a 4-20 mA output used to control a pump motor speed. A recent failure of a flow sensor brought the process skid instrumentation to my company's quality manager's attention. He asked how we know that the temperatures, pressure and flow are accurate, and how do we know that we are cleaning properly.
I've been tasked to write a procedure for troubleshooting, calibrating and testing the 4-20 mA instruments on the skid. I can probably stumble through this, but what are some best practices for troubleshooting the analog…

Most public utilities deliver basic power and water, and God bless them for doing it. However, a few go beyond their essential missions, and seek to further enhance the overall well-being and prosperity of their communities.
One of these is…

Advanced control on fuel and steam can control emissions while saving millions.

It’s no secret that advanced process control (APC) has played a major role in the process industries for many decades. However, while many organizations focus only on major process units, there’s often an untapped opportunity to do more, and…

Our readers tell us who they think delivers the best technology in our industry

There's knowledge in our readers. That's why every year we ask our loyal audience to help us determine which automation service providers offer the best products and brands they can rely on to get the best combination of performance, ease of use,…

Just when it seems like today’s sophisticated motors and drives can’t possibly add more efficiencies and capabilities, engineers conjure up new tricks and refinements, followed by end users and system integrators who materialize new settings and…

Control's monthly guide brings you invaluable industry information to stay up to date on the latest trends and developments.

THE CLASSIC VALVE BOOK
The fourth edition of the 295-page classic text, "Control Valve Handbook," by Fisher Controls International and Emerson Process Management reports this classic text has been a primary reference since its first printing in1965.

Control's monthly guide brings you invaluable industry information to stay up to date on the latest trends and developments.

THE CLASSIC VALVE BOOK
The fourth edition of the 295-page classic text, "Control Valve Handbook," by Fisher Controls International and Emerson Process Management reports this classic text has been a primary reference since its first printing in1965.

Just when it seems like today’s sophisticated motors and drives can’t possibly add more efficiencies and capabilities, engineers conjure up new tricks and refinements, followed by end users and system integrators who materialize new settings and…

Actionable information is essential for the effectiveness of the 'loop,' as it is for closed-loop control and open-loop alarms.

When I sat down in my office this morning, I was greeted by the operations manager, who pointed out an entry from last night’s operations log: “Did you see? The boiler steam vent is in manual because the pressure reading whacked out and made the…

Actionable information is essential for the effectiveness of the 'loop,' as it is for closed-loop control and open-loop alarms.

When I sat down in my office this morning, I was greeted by the operations manager, who pointed out an entry from last night’s operations log: “Did you see? The boiler steam vent is in manual because the pressure reading whacked out and made the…

Actionable information is essential for the effectiveness of the 'loop,' as it is for closed-loop control and open-loop alarms.

When I sat down in my office this morning, I was greeted by the operations manager, who pointed out an entry from last night’s operations log: “Did you see? The boiler steam vent is in manual because the pressure reading whacked out and made the…

Our readers tell us who they think delivers the best technology in our industry

There's knowledge in our readers. That's why every year we ask our loyal audience to help us determine which automation service providers offer the best products and brands they can rely on to get the best combination of performance, ease of use,…

Visualizing and contextualizing safety data can have a positive impact on productivity and compliance.

"Information is one thing, but safety information is quite another," says George Schuster. He should know. He’s charged with business development for the Global Safety Team of Rockwell Automation and has seen many plants and factories begin to…

How to deal with the constraints of putting access points in hazardous areas.

In an ideal world, it wouldn’t be necessary to worry about explosive atmospheres. Unfortunately, plant environments are far from ideal, with most process plants being about 80% Class I, Div. 2 (Zone 2) and another 10% Class I Div. 1 (Zone 1), so…

Key is to learn as much as possible to make digital technologies safe, secure and successful in process settings.

As usual, and I’m sure this is true for many of you, this year’s autumn season has been a frantic dash of work, deadlines, sleep deprivation, indigestion and suspiciously arthritic stiffness. In my case, this means covering all sides of the…

With today’s network technology, even Ethernet and wireless are almost always fast enough.

As automation professionals, one issue we have about control loops is ensuring we're able to support real-time control. Historically, when Ethernet was 10 MB/s and there were multiple drops on a single port, collisions were a significant concern and…

With today’s network technology, even Ethernet and wireless are almost always fast enough.

As automation professionals, one issue we have about control loops is ensuring we're able to support real-time control. Historically, when Ethernet was 10 MB/s and there were multiple drops on a single port, collisions were a significant concern and…

Because they're the crossroads, nexus and Grand Central Station for sensor signals and data arriving and requests and actuation instructions departing, it's a big help that I/O and terminal blocks are more flexible and capable than ever.

Compact, Remote I/O for Zone 2/Div 2
LB System remote I/O has more power in less space with high-performance, compact modules plugged into a backplane. Energy-saving power management and low-power dissipation allow maximum packing density. With the…

Be just 33 seconds more productive each hour, and the savings mount quickly.

Rockwell Automation previewed its new, forward-looking App Platform for mobility at this week’s TechED conference in Orlando. While focused first on redefining smartphone use on the plant floor – with the aim of making individual workers more…

Control’s latest State of Technology report delves into the many aspects of power systems of interest in process plants.

From sourcing and ensuring uninterrupted flows of clean electricity to monitoring, regulating and metering generation and consumption throughout a facility, process automation professionals who want a smooth-running, efficient and reliable facility are well advised to seek and control power.
This anthology of recent articles delves into the many aspects of power systems of interest in process plants. Remote and wireless systems are speeding development and standardization of energy harvesting and improved battery systems.
Line-powered supplies that used to only transform electricity and maybe offer surge protection are now monitoring and measuring current and voltage profiles, implementing alerts and alarms, and sending data up to…

Greg: Here we take advantage of the chance to talk to Bill Thomas, who provides a great lesson of how to succeed in advancing capabilities and opportunities in his career and the control systems for which he was responsible. His career and the…

Control's monthly guide brings you invaluable industry information to stay up to date on the latest trends and developments.

AT THEIR BEST, ALL THE TIME
ExperTune’s white paper, “How to Improve Performance of Process Control Assets,” by George Buckbee, P.E., describes the practice of real-time asset performance management, shows how to get assets to perform at their best all the time, and demonstrates the value of integrating these tools for a performance picture that delivers financial results. It’s available here.
ISA / www.isa.org
ANALYZING, PREDICTING PROBLEMS
This 57-minute video, “Avoid Equipment Surprises: Predictive Diagnostics for Oil & Gas,” is presented by Joe Dupree, GE Automation and Controls, and users from NiSource Gas and Alyeska. They demonstrate condition-based monitoring, predictive analytics and other tools for evaluating…

Steve Christian remembers the days—not too long ago—when production schedules were printed on sheets of paper and distributed to operators at his plant, who would manually twist valve handles to send the Ragu sauce tomato slurry from one kettle…

Advanced control on fuel and steam can control emissions while saving millions.

It’s no secret that advanced process control (APC) has played a major role in the process industries for many decades. However, while many organizations focus only on major process units, there’s often an untapped opportunity to do more, and…

Find and slay the dragons lurking in the typical safety instrumented system.

Cybersecurity is a growing concern in the process industries, and a number of good articles have been written about it for industrial control systems (ICS)—many full of doom and gloom. Here, we will divide the ICS into two parts: safety…

Big data can only help users if they understand what it is, how it can affect their controls and processes, and how they can use it to optimize operations.

Similar to any new technology emerging on the process control front, big data can only help users make better decisions if they understand what it is, how it can affect their controls and processes, and how they can use it to optimize operations.

Our readers tell us who they think delivers the best technology in our industry

There's knowledge in our readers. That's why every year we ask our loyal audience to help us determine which automation service providers offer the best products and brands they can rely on to get the best combination of performance, ease of use,…

Deaerator Level Control

Can a P Controller Be Replaced With a Linear Function Generator in Controlling the Level on a Deaerator?

Therefore, as shown in Figure 1, the two-controller system will "bump" the valve by the amount of the offset when the loop is switched between manual and automatic, but this does no harm to the level control, and the operator should simply be educated to accept it.

Another option is to provide logic that guarantees bumpless transfer, but it will not improve the quality of level control, only eliminate the "offset bump."

A: I'm guessing that the current implementation does not use true P controllers. Digital systems based on incremental (velocity) algorithms have a floating output bias that changes whenever the controller is placed in manual or hits a limit. True proportional control is what you need, and you can get it with simple linear functions. The only caveat is that you can't transfer bumplessly from manual to auto. But it will control level. Teach the operators to accept the variable offset.

A: It sounds to me like the P controllers rebalance their bias term when the controller is in manual mode. Some control systems allow the option of disabling the bumpless rebalance. (I do not know what is meant by "tripping" to manual, or what would cause that. A boiler trip to no fire? The deaerator level must always be controlled, no? A leaking valve could fill or drain it.)

If the disable option does not exist, by all means use linear function generators (characterizers) to provide the required control action.

I'd build in some dead band, so that the valve does not creep off its seat near zero. Let it get a few percent away from zero output, and then pop it open to the required percent. Do this by putting a kink in the function. This is not usually possible in a P controller.

The function generator will not provide any way to rebalance during manual mode. Even if it did, the rebalance is not desired because it would bias the function, as it does now with the P controllers. That is, you do not want bumpless transfer to a calculated value. The operator should adjust the valve to the calculated value before resuming automatic operation. Actually, this will work with the P controllers, if the bias value is displayed, so that the operator can manually adjust the output to make the bias value go to zero.

Foundation fieldbus control blocks use a timed ramp to bring the manually set output back to the calculated value on transition to auto. This provides a bumpless transfer that uses the ramp to bring the valve to the calculated value without adding a permanent (until the next transition to manual) bias. Perhaps blocks are available to do this in the control system that is being used.

If the number of function blocks is not constrained, another way to solve this is to build two function generators, and connect a PI valve position controller between the function output and the valve. If the operator needs manual control of the valve, the PI will rebalance to zero error at the integral rate when automatic control is restored.

Some controllers have a feature called "setpoint tracking" (some manufacturers call this "PV tracking"). This means that the setpoint does not remain constant always, but when the controller is in manual, the SP is forced to whatever the current PV is. So when the operator changes back to auto, the SP and PV are already equal, hence there is no "error," therefore, no change in valve position. This is one way of achieving bumpless transfer, but it is not the only way.

I assume—and hope—that you do not have setpoint tracking on your system. If the operator sets a setpoint of 40% (displayed as 142 mm), then that setpoint stays there. If this is the case, bumpless transfer must be achieved in some other way.

A proportional control algorithm first determines the error (SP - PV, for a reverse acting controller-makeup valve) or (PV - SP, for a direct-acting valve-surplus loop), where both PV and SP are in % of measurement value. (That is, 142 mm = 40% of 355 mm, 213 mm = 60% of 355 mm. Then the controller output is computed as (controller gain x error + an added value which I will call "bias"). This "bias" is an operator-adjustable setting on some controllers; on others it is not. In essence, the bias value is the signal sent to the valve when the controller is in auto and the SP and PV are equal.

The manual-auto switch comes after the normal control algorithm, so in what follows, I will talk about two different outputs:

The controller output, which is the signal sent to the valve, whether the controller is in Auto or Manual

The control algorithm output, which is the computed output that is used if the controller is in Auto.

Consider the make-up controller. You want the controller output to be 0% (valve closed) when the PV is at 40% (142 mm). At that point, there is 0% error, so the bias value should be 0%, and it should never be changed; that is, you do not want bumpless transfer.

Consider this. Suppose the level is at 71 mm (20%). The error is 20%. (SP is at 142 mm, or 40%. SP - PV = 40% - 20% = 20%.) If the controller is in Auto, the controller output would be Error x Gain + Bias = 20% x 2.5 + 0% = 50%. But suppose the controller is in manual and the operator has set some other value for valve position, say 55%. In order to have bumpless transfer, the controller has to change the bias to 5%, so that the control algorithm output matches his manual setting. (Error x Gain + Bias = 20% x 2.5 + 5% = 55%). Now, when PV = 40% (the SP) the valve will be 5% open, not 0 % open, as you desire.

If you did not have bumpless transfer, in the situation above (the PV is at 71 mm, the controller is in manual, and the operator-set valve position is 55%), when the operator goes to auto, the valve position will go to 50%. There will be a bump, but the operator will know what the controller is doing at all times.

Going to a linear function generator will not help. A proportional controller without bumpless transfer is already a linear function generator. Going to a linear function generator, then implementing the logic for bumpless transfer will get you right back to the place you are now.

I would seriously consider why the system ever trips to manual. What has gone wrong to cause that. Could there be additional controls that would mitigate these circumstances? I'm thinking of something like a feed-forward action here. I think there should be an in-depth analysis of the entire system, plus some operator training. I have seen cases where operator understanding of the system went a long ways toward solving problems.

A: The control scheme that you describe is a bit different than what we would typically implement for deaerator level control. In our implementation we would use a single level controller whose output would drive the two valves in a split-range fashion. In some applications, we would also add a feed-forward to the controller based on deaerator outlet flow. If the specification for your control scheme is as you describe, however, there is no reason why you could not use linear function generators in place of the proportional-only controller if you provide the manual-auto transfer related functions with additional logic.